This section is intended to provide a background or context to the invention recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Mining shovels are often powered by hydraulic pressure systems. In these systems, hydraulic fluid is transmitted throughout the machine to various actuators, or hydraulic cylinders, where the fluid is converted into energy for powering the machine's components as necessary. For instance, the dipper assembly may be powered by one or more actuators. Typically, an operator will provide a command to the actuator via a control system, retracting or extending the cylinder in order to move the dipper assembly. The actuators may be used to apply a crowding force into a bank of material, filling the dipper with material.
When the dipper is filled with material, the dipper assembly may move without an operator command due to the weight of the dipper load, inadvertently extending or retracting the cylinder. When this occurs, a chamber of the cylinder may expand, creating a void in the cylinder. When the dipper assembly is moved by operator command, a source of fluid may be manually or automatically provided to fill the void and prevent cavitation. However, during a static condition (i.e. when the dipper assembly moves without an operator command), fluid is not typically provided without an operator command to fill the void, often leading to a cavitation within the cylinder. Cavitation within a hydraulic system can cause unwanted noise, damage to the hydraulic components, vibrations, a loss of efficiency, and can reduce the useful life of the system and its components.
Conventional mining shovels may include an independent metering valve for controlling the flow of hydraulic fluid from a pump to a hydraulic cylinder. An example of such a conventional independent metering valve can be found in U.S. Pat. No. 5,960,695 issued Oct. 5, 1999, for “System and Method for Controlling an Independent Metering Valve,” which discloses an independent metering valve that includes four independently operable, electronically controlled metering valves to control fluid flow between a pump and hydraulic cylinder. This conventional independent metering valve is not controlled to automatically respond to void conditions with the hydraulic cylinder, and the associated cylinder is susceptible to voiding and/or cavitation when no operator command is given.